A conventional acceleration sensor is described with reference to FIG. 20. The conventional acceleration sensor comprises the following elements: rigid substrate 101, base glass 102 placed on rigid substrate 101, flexible substrate 103 placed on base glass 102, weight 104 placed on the underside of flexible substrate 103, glass substrate 105 placed above and confronting flexible substrate 103, and opposed electrodes 106 placed on respective opposed faces of flexible substrate 103 and glass substrate 105 (disclosed in Patent Document 1).
The way of detecting acceleration with the foregoing sensor is described hereinafter. When acceleration occurs, weight 104 is going to move along an accelerating axial direction, so that flexible substrate 103, to which weight 104 is attached, is somewhat bent. Then the distance between flexible substrate 103 and glass substrate 105 changes, whereby an electrostatic capacity between opposed electrodes 106 is varied. The sensor thus detects the acceleration based on the variation caused by the change in the distance between opposed electrodes 106.
The acceleration sensor discussed above is placed, corresponding to an axis to be sensed, in an attitude control device or a navigation system of mobile carriers such as vehicles.
Although the sensor detects acceleration based on a change in the capacity between opposed electrodes 106, weight 104 tends to change its place along Z-axis because weight 104 is placed on the underside of flexible substrate 103 such that weight 104 floats in midair and above rigid substrate 101.
For instance, if weight 104 moves along Z-axis such that opposed electrodes 106 become away from each other, the electrostatic capacity between opposed electrodes 106 becomes smaller. When acceleration along X-axis or Y-axis occurs in this state, a change in the electrostatic capacity between opposed electrodes 106 becomes smaller than a supposed one, so that a detection accuracy of the acceleration along X-axis or Y-axis is degraded.
Next, another conventional sensor for detecting angular velocity and acceleration is described hereinafter. This sensor is disclosed in, e.g. patent document 2 and patent document 3.
A sensor dedicated to angular velocity or a sensor dedicated to acceleration has been used for detecting the angular velocity or the acceleration independently. Various electronic devices, which need to detect both of angular velocity and acceleration, should be thus equipped with multiple sensors mounted on the substrate for detecting acceleration and angular velocity respectively.
The angular-velocity sensor, in general, senses a distortion of a detecting element electrically, thereby detecting angular velocity. The detecting element shapes like a tuning fork, H-shape, or T-shape, and vibration of this detecting element produces Coriolis force, which is accompanied by the distortion of the detecting element. On the other hand, the acceleration sensor, as previously discussed, includes weight 104, and acceleration is accompanied by movement of weight 104. The sensor then compares the movement with a state prior to the movement, thereby detecting acceleration.
The angular-velocity sensor and the acceleration sensor discussed above are placed, corresponding to an axis to be sensed, in an attitude control device or a navigation system of mobile carriers such as vehicles. However, the foregoing structure needs a space on a substrate for mounting both of the angular-velocity sensor and the acceleration sensor corresponding to the axes to be sensed, where angular velocity and acceleration are supposed to occur. As a result, the electronic device has resisted being downsized.
Patent Document 1: Unexamined Japanese Patent Application Publication No. H10-177034
Patent Document 2: Unexamined Japanese Patent Application Publication No. 2001-208546
Patent Document 3: Unexamined Japanese Patent Application Publication No. 2001-74767